The present invention relates to an engine powertrain control device in which torque is estimated by computation and to a control method for a vehicle having an engine powertrain consisting of an engine and an automatic transmission.
An engine powertrain is controlled by obtaining an output shaft torque of a torque converter of an automatic transmission and reducing fluctuations in the output shaft torque, thereby reducing a shift shock upon gear shifting.
As a known method of obtaining the output shaft torque of the torque converter, the torque is directly detected by of a torque sensor or estimated from other information by computation.
A torque estimating method is described in Japanese Patent Laid-open No. Hei 4-8961, for example, wherein the output shaft torque of the torque converter is estimated by using rotating speeds of input and output shafts of the torque converter and characteristics of the torque converter. The torque converter characteristics are a pump capacity coefficient and a torque ratio. Data of the pump capacity coefficient and data of the torque ratio are separately stored in the form of data table in a memory such as a ROM (Read-Only Memory) provided in a control device, as functions of a speed ratio which is a ratio between the rotating speeds of the input and output shafts of the torque converter. In performing the computation of the output shaft torque of the torque converter, the separate pieces of stored data are retrieved to be used.
In the prior art mentioned above, the data of the pump capacity coefficient and the data of the torque ratio are separately stored in the memory. Accordingly, the capacity of the memory must be enlarged. Further, each piece of data is stored as discrete values in the data table, so that interpolation between adjacent values is required. To reduce an error due to the interpolation, the space between the adjacent values must be reduced to increase the amount of the data, causing a further increase in the memory capacity.
As an alternative method, it is considered to store the data in the form of a functional expression rather than in the form of the data table. In the case of approximating actual values by using the functional expression, a high-order functional expression must be used in order to avoid large differences between calculated values by the functional expression and the actual values. However, it is difficult to find out an optimum functional expression that can make the calculated values coincide well with the actual values.
It is accordingly an object of the present invention to provide an engine powertrain control device and control method which can reduce data amounts of characteristics of a torque converter to be used for estimation of the output shaft torque of the torque converter.
According to the present invention, there is provided an engine powertrain control device comprising apparatus for detecting or computing rotating speeds of input and output shafts of a torque converter, apparatus for computing a speed ratio as a ratio between the rotating speed of the input shaft and the rotating speed of the output shaft of the torque converter obtained above, a memory for storing data of a pump capacity coefficient and a torque ratio product, c.times.t, obtained by multiplying a pump capacity coefficient c and a torque ratio t of the torque converter and for retrieving or computing a value of the product, c.times.t, corresponding to a value of the speed ratio computed above, and apparatus for computing an output shaft torque of the torque converter by using the value of the product, c.times.t, obtained above.
The rotating speeds of the input and output shafts of the torque converter are detected by mounting rotating speed sensors near the input and output shafts to directly detect the rotating speeds with the rotating speed sensors. Alternatively, the rotating speeds of the input and output shafts are computed by using any sensors other than the rotating speed sensors. The speed ratio computing apparatus computes a speed ratio as a ratio between the rotating speeds of the input and output shafts of the torque converter obtained above. The storing and computing apparatus storing data of a pump capacity coefficient and torque ratio product, c.times.t, retrieves a value of the product, c.times.t, corresponding to a value of the speed ratio obtained above. The torque converter output shaft torque computing apparatus computes a torque converter output shaft torque by using the value of the product, c.times.t, obtained above and the torque converter input shaft rotating speed obtained above. As described above, the storing and computing apparatus stores data of the pump capacity coefficient and torque ratio product, c.times.t, rather than separately storing data of a pump capacity c and data of a torque ratio t which are functions of the speed ratio. Accordingly, a memory capacity can be reduced to half. When in the past a value of the stored data is obtained by interpolation so that the data of the pump capacity coefficient c and the data of the torque ratio t are separately stored, an error occurred due to interpolation for each data. Accordingly, in computing the product, c.times.t, an even larger error occurred because of multiplication of the two interpolated values each having the initial error. To the contrary, according to the present invention, interpolation is made by using the data of the product, c.times.t, previously stored, so that the error due to the interpolation can be reduced over that in the prior art, thereby allowing torque estimation with high accuracy.